Dissipation of static electricity

ABSTRACT

Disclosed is a method of imparting static dissipation efficacy to flooring otherwise incapable of dissipating static electricity to any practical extent. The flooring is covered at one or more chosen positions with a fabric, conveniently in the form of a &#39;&#39;&#39;&#39;throw rug&#39;&#39;&#39;&#39; or other similar structure, which fabric contains yarns comprising electrically conductive material. An efficient dissipation of high concentrations of static electricity accumulated by humans is effected by a simple stepping or walking upon the throw rug.

United States Patent 1 Koeleveld et al.

[54] DISSIPATION OF STATIC ELECTRICITY [73] Assignee: Dow Badische Company, Williamsburg, Va.

[22] Filed: Feb. 9, 1971 [21] Appl. No.: 113,865

[ 51 Mar.27,1973

Primary Examiner-L. T. Hix Attorney-George F. Helfrich [57] ABSTRACT Disclosed is a method of imparting static dissipation efficacy to flooring otherwise incapable of dissipating static electricity to any practical extent.

The flooring is covered at one or more chosen positions with a fabric, conveniently in the form of a throw rug" or other similar structure, which fabric contains yarns comprising electrically conductive material. An efficient dissipation of high concentra- U-S- Cl. R, 3 C tions of static electricity accumulated humans is cf. [51] Int. Cl ..II05f 3/00 fe ted by a simple stepping or walking upon the throw [58] Field of Search ..317/2 R, 2 C rug,

[56] References Cited 1 Claim, 1 Drawing Figure UNITED STATES PATENTS 3,288,175 11/1966 Valko ..3l7/2 C l0 9 A1 3 v 7 J VOLTAGE s C (KV) i TIME(SEC.)

Patented March 27, 1973 0 Q I!) N l o w o w 9 co 10 re N 0 Lu 0 i 55 INVENTORS FRANS P. KOELEVELD REGINALD MAK NGO RUSSELL s. DUBY k IR A TORNEY T|ME(SEC.)

DISSIPATION OF STATIC ELECTRICITY SUBJECT MATTER This invention relates to textiles in general, and in particular to floor coverings for use in the dissipation of accumulations of static electricity by human beings.

PRIOR ART The accumulation of static electricity by human beings as a result of contact with textile fabrics is a phenomenon which has commanded the attention of the textile industry for quite some time. This phenomenon has been a cause not only of vexation and discomfort (e.g. one experiences an unpleasant jolt or shock upon touching a metal doorknob after having walked across a nylon carpet), but also of danger e.g. discharges of static electricity often result in sparks capable of igniting flammable mixtures such as ether/air, which are commonly found in hospitals, especially in operating rooms).

Accordingly, many expedients have been proposed for avoiding the accumulation of high concentrations of static electricity. Of these, the most satisfactory, with respect to their efficiency and permanence, are those which comprehend the utilization of fibers possessing electrical conductivity (especially metal fibers, and more advantageously, metallic laminate filaments) in combination with common natural and/or synthetic fibers to produce a woven, knitted, netted, tufted, or otherwise fabricated structure, the utilization of which results in no undesirable buildup of static electricity. Some of the more noteworthy of these methods and structures may be found in U.S. Pat. Nos. 2,129,504;

, 2,714,569; 3,288,175; and 3,069,746; in Webber,

Metal Fibers, Modern Textile Magazine, May, 1966, pp. 72-75; and in particular, in U.S. patent application Ser. No. 635,0l4, filed May 1, 1967, and in the U.S. Patent Application of C. E. Lowry, W. J. Gilbertson, and J. A. Gusack, filed on Nov. 27, 1970, for Laminate Filament and Fabric Prepared Therefrom.

These expedients, howsoever efficacious, do not encompass the utilization of fabric structures already being employed, but rather require their removal and the succeeding replacement thereof with the structures newly specified and defined. By way of example, an existing nylon carpet, the use of which in an atmosphere of low relative humidity results in the accumulation of high concentrations of static electricity by persons contacting it, is removed and replaced with a completely new carpet comprising metallic laminate filaments in the pile thereof, the use of which carpet under the same atmospheric conditions does not result in an undesirable buildup of static electricity by those who contact it.

That such expedients represent significant advances in the art is in no way disputed. However, the utilization of such expedients is often resisted or postponed because of the expense and inconvenience attending the partial or total replacement of existing. structures, particularly those which have been purchased only recently.

SUMMARY OF THE PRESENT INVENTION Accordingly, it is an object of this invention to pro-- vide an economical, convenient, rapid, and innocuous expedient for the elimination of the undesirable effects of high concentrations of static electricity which have been accumulated by humans as a result of their contact with textile fabrics. It is a further object of this invention to provide a method of imparting static dissipation efficacy to flooring otherwise ineffectual in the dissipation of static electricity, which method does not requirethe removal of any of the existing flooring.

in accordance with the present invention, these objects and benefits are achieved by the practice of a method which comprises covering the flooring having poor static dissipation properties with a textile fabric containing yarns comprising electrically conductive material. The fabric, which is produced according to any of the standard weaving, tufting, knitting, netting, or braiding techniques, is most advantageously in the form of a throw rug" or other similar structure, which is conveniently spread out upon the exposed surface of the existing flooring at chosen sites near points of ingress and egress to rooms, compartments, elevators, etc., and at other locations where contact by the human body with electrically grounded objects is likely to occur. High concentrations of static electricity, which have been built up on humans as a result of their contact with existing flooring and/or other materials having poor static dissipation properties, such as automobile seat covers, are readily and innocuously dissipated, to a level below that which can result in discomfort, by contact of the body with the throw rug containing fibers comprising electrically conductive material. This contact is usually and advantageously supplied by a simple touching of the surface of the throw rug with both feet of the body, as for example, is normally provided by a walking or stepping upon the fabric. Any subsequent contact of any parts of the body with electrically grounded objects does not cause annoyance or discomfort, if such contact is made before the body has built up any significant additional concentration of static electricity. It is clear, of course, that such an additional, significant concentration of static electricity could result from substantial further contact with fabrics having poor static dissipation characteristics after contact with the throw rug has been made. In view of this, a determination can be made concerning the number and location of throw rugs necessary to effectively eliminate the annoyance and discomfort resulting from accumulations of static electricity in any particular area.

BRIEF DESCRIPTION OF THE DRAWING For a more complete understanding of the present invention, including its objects and benefits, reference may be made to the detailed description set forth below, which should be read in the light of the accompanying drawing, wherein:

The FIGURE is a plot of experimental observations depicting the relationship between the electrostatic voltage accumulated by a human being and the time elapsed as he walks at a constant rate upon certain floor coverings under particular atmospheric conditions.

With particular reference to the drawing, the experimental data used to prepare the plot were obtained as follows: A test room was provided having a concrete floor which was completely covered by a 16 oz. per square yard bulked continuous filament nylon tufted pile carpet. The room, which had an area of greater than 100 square feet, was at a temperature of about 73 F., and the relative humidity therein was about 20 percent. A small metallic ground plate, which was positioned beside the test section of the nylon carpet, was connected electrically through the flooring to the electrical ground of the building.

Also provided was a throw rug comprehended by the present invention. This throw rug, which had dimensions of 2 feet by 3 feet, was a 30 oz. per square yard pile fabric produced by tufting into a jute backing material, using standard tufting techniques, a yarn prepared by twisting two ends of 2/1 cotton count acrylic yarns with a single strand of a metallic laminate filament having an aluminum ply and 2 polyethylene terephthalate plies bonded to opposite sides of the aluminum ply, the structure and method of preparation of the metallic laminate filament being that set forth in US. patent application Ser. No. 635,014, filed May I, 1967. The metallic laminate filaments were employed in an amount of 3.0 percent by weight, based upon the total weight of the yarn forming the pile'. The metallic laminate filaments had a width of 0.01 inches and a denier of about 150. The throw rug was simply spread out upon the outer surface of the nylon carpet at an arbitrary position thereon.

Holding a hand probe, which was connected to an electrostatic detection head, a human operator commenced Test No. l of this Example, which required him to. walk normally on the nylon carpet at a'constant rate of approximately 2 steps per second for a period of 7.5 seconds, exercising care not to touch the ground plate, throw rug, or other objects in the room, andnot to rub or scuff his shoe soles on the carpet. The static electricity accumulated was continuously measured and recorded, and the results were plotted, forming the curve OAB of the drawing. As revealed by curve OAB, the static electricity accumulated by the operator increased to a maximum after about 5 seconds of elapsed time, i.e., after about steps on the carpet had been taken, whence no significant increase or decrease resulted as the operator continued to walk on the nylon carpet. This steady state maximum, which was approximately l2 KV, is considerably above the threshold level of human sensitivity, such being generally set at about 3 KV. Consequently, the operator received a severe shock upon touching a rnetaldoorknob in the "room at the completion of this test.

In Test No. 2 of the series of tests which make up this Example, the same operator commenced walking on the nylon carpet under the same conditions prevailing in Test No. l, the static electricity accumulated being continuously measured and recorded as in Test No. 1. After an elapsed time of 5 seconds, i.e., after 10 steps had been taken, the operator stopped walking and stood perfectly still on the nylon carpet. The accumulation of static electricity on the body of the operator was 4 measured continuously while he was standing still on the nylon carpet and the results were recorded. Curve OAC of the drawing is a plot of the results of; Test No.

' 2, from which it can be seen that ineffectual dissipation extent, with particular reference to the threshold level of human sensitivity.

In Test No. 3 of this series of tests, which test is illustrative of the results achieved by employment of the present invention, the same operator commenced walking on the nylon carpet under the same conditions prevailing in Test No. I, the static electricity accumulated being continuously measured and recorded as before. After 10 steps had been taken on the nylon carpet, the operator stepped immediately upon the throw rug specified above in this example, and continued to take steps thereon at -second intervals. Curve OAD of I the drawing is a plot of the results of Test No. 3, from which it can be seen that a significant dissipation of an accumulation of static electricity is afforded by a stepping upon a throw rug or similar structure according to the instant invention, which stepping upon began at point A and continued through point D. As seen from segment AD of curve OAD, the dissipation of accumulated static electricity is effected from a point considerably above the threshold level of human sensitivity to a point below this level after only about 2 steps upon a throw rug according to the present invention (about 1 second of elapsed time thereon). At the conclusion of Test No. 3, the operator received no annoying shock upon touching a metal doorknob from his position on the throw rug. 7

In Test No. 4 of this series, the same operator commenced walking on the nylon carpet under the same conditions prevailing in Test No. I. When the elapsed time reached 5 seconds, i.e., when 10 steps had been taken, the operator stepped upon the ground plate. Curve OAE, which is a plot of the results of Test No. 4, shows the complete discharge resulting from contact with an electrically grounded object.

EXAMPLE 2 This example, which is not illustrative of the practice of the present invention, is set forth for comparative purposes only. I-Ierein a procedure was followed which was identical in all aspects to that employed in Test No. 3 of Example 1, except that the throw rug utilized was a 30 oz. per square yard pile fabric produced by tufting into ajute backing material, using standard tufting techniques, a yarn prepared by twisting two ends of 2/1 cotton count acrylic yarns; i.e,, no metallic laminate filaments or other electrically conductive material was present in the rug. At the conclusion of this test, i.e., after 5 steps had been made by the operator upon the throw rug, the accumulated static charge in' the body of theoperator was approximately 8 KY, which is substantially above the threshold level of human sensitivity. The operator received a severe shock upon touching a metal doorknob from his position on the rug at the completion of this test.

EXAMPLE 3 This example, which is illustrative of the results of practicing the present invention, employed a procedure identical in all aspects to that followed in Test No. 3 of Example 1, with the exception that after taking steps upon the nylon carpet, the operator took only 2 steps on the throw rug according to the present invention, followed by 3 steps upon the nylon carpet again. The accumulated static electricity on the body of the operator was less than 3 KV at this point and the operator received no annoying shock upon touching a metal doorknob from his position on the carpet at the completion of the test.

EXAMPLE 4 In this example, which is illustrative of the results achieved by practicing the present invention, a

procedure was followed which was identical in all aspects to that employed in Test No. 3 of Example 1,

' except that the throw rug utilized was a 2 ft. by 3 ft.

tor received no annoying shock upon touching a metal doorknob from his position on the throw rug.

EXAMPLE 5 This Example, which is not illustrative of the present invention, is set'forth for comparative purposes only. The procedure employed herein was identical in all aspects to that employed in Test No. 3 of Example No. l, with the exception that a l ft. by 3 ft. sheet of aluminum foil having a thickness of 0.001 inches was employed in place of the throw rug according to this invention. The foil is commercially available under the trademark REYNOLDS WRAP. At the conclusion of this test, the static electricity accumulated on the body of the operator was well above the threshold level of human sensitivity, and the operator received a severe shock upon touching a metal doorknob from his position on the aluminum sheet.

EXAMPLE 6 In this example, which is illustrative of the present invention, a series of tests were run, each employing a procedure identical to that employed in Test No. 3 of Example 1, with the exception that the throw rugs specified below were individually employed in the below-identified tests:

Test No. Throw Rug 1 A 2 ft. by 2 ft. tufted pile fabric of acrylic yams, the fabric having in the pile thereof 3.0 weight per cent of the same metallic laminate filaments employed in the throw rug of Example 1.

2 Same as Test No. 1 above, except that the dimensions of the throw rug were 3 ft. by 5 ft.

3 Same as Test No. 1 above, except that the dimensions of the throw rug were 4 ft. by 6 ft.

In all tests of this example the static electricity accumulated by the operator was reduced to a value below the threshold level of human sensitivity and the operator received no annoying shock upon touching a metal doorknob from his position on the throw rug at the completion of each test.

EXAMPLE 7 In this example, which is illustrative of the present invention, a series of tests were run, each employing a procedure identical to that employed in Test No. 3 of Example 1 above, with the exception that the throw rugs specified below were individually employed in the below-identified tests:

Test No.

In all tests of this example the static electricity accumulated by the operator was reduced to a value below the threshold level of human sensitivity and the operator received no annoying shock upon touching a metal doorknob from his position on the throw rug at the completion of each test.

It is obvious to one of skill in the art upon an examination of the foregoing examples, that the method comprehended by the present invention is employed to impart static dissipating efficacy to any flooring at chosen positions thereon, the flooring being otherwise incapable of dissipating static electricity to any practical extent; i.e., the flooring being otherwise incapable of dissipating the accumulated static charge to a value below the threshold level of human sensitivity. lllustrative examples of such a flooring are, in addition to the nylon carpeting specified in the above examples, carpets comprising fibers of acrylonitrile polymers, polyethylene terephthalate polymers, natural wool fibers, and other common, non-conductive, natural and synthetic fibers available in the industry today; plastic tile is also illustrative of a common flooring having poor static dissipation properties.

The fabric employed in the method of the present invention may be any textile structure produced by standard weaving, tufting, knitting, netting, or braiding techniques. It is advantageously in the form of a throw rug" or similar structure, which is conveniently carried from place to place and simply laid out upon the surface of the flooring at any desired location. Such throw rugs generally have dimensions of from 2 ft. by 2 ft. to 4 ft. by 6 ft., although larger ones (e.g. having an area of about 50 square feet) have been found useful.

Electrically conductive material present in the yarn which makes up the fabric, which material is advantageously in the form of metal wires, metal fibers or this laminate filament is twisted with two ends of 2/1 cotton count acrylic yarns, a yarn is produced which is I advantageously tufted into a jute backing material to filaments, or metallic laminate filaments, has been found efficacious in the practice of the present invention when its concentration is aslow as about 0.1 per cent by weight, with the remainder of the yarn comprising any of the useful natural and synthetic fibers and filaments employed in the textile industry today. The upper limit of the amount of electrically conductive material employed is determined primarily by economic considerations. Metallic laminate filaments as specified herein have been found useful in amounts of 90 percent by weight. Examples of fibers and filaments advantageously combined with the electrically conductive material are those prepared from acrylonitrile polymers, nylon polymers, polyethylene terephthalate polymers, as well as those of wool and cotton.

A preferred embodiment of the present invention encompasses the utilization of a throw rug which is pile fabric, the pile comprising yarns of acrylic fibers combined with from about 0.5 to about 9.0 per cent by weight of laminate filaments defined in and prepared according to U.S. patent application Ser. No. 635,014,

filed May 1, 1967. Specifically, these laminate filaments comprise an electrically conductive ply, which is advantageously the metal aluminum, and at least one polymeric ply, which is advantageouslypolyethylene terephthalate. Two polymeric plies, each bonded to opposit'e sides of the electrically conductive ply, are most advantageously employed. It has also been found of particular advantage to employ a metallic laminate filament having a width of about 0.01 inches and a denier of between about 130 and 210. When a single strand of prepare the pile fabric comprehended by the preferred embodiment of this invention. As will be understood by one of skill in the art upon a reading of the foregoing portions of this detailed description, it is not necessary that every end of yarn in the pile contain a strand of the metallic laminate filament. Moreover, more than one strand of metallic laminate filament per end of yarn in the pile may be advantageous, especially under conditions of very low relative humidity.

As is immediately clear to one of skill in the art, it is possible to remove a small section of a flooring having poor static dissipation properties and to insert in place thereof a throw rug according to the present invention. That such a practice is not necessary is revealed by the present invention. Moreover, there is no practical adthe accumulation of stati c to levels exceeding the threshold of human sensitiv ty m human beings contacting said flooring, which method comprises covering said flooring at a chosen position thereon with'a throw rug which comprises yarns comprising electrically conductive material. 

1. A method of imparting static dissipating power to flooring which is otherwise ineffectual in preventing the accumulation of static to levels exceeding the threshold of human sensitivity in human beings contacting said flooring, which method comprises covering said flooring at a chosen position thereon with a throw rug which comprises yarns comprising electrically conductive material. 